This invention relates to systems for synchronizing the supply of gas by a respirator with spontaneous respiration. More specifically, this invention relates to a method and apparatus for controlling a respirator in order to synchronize the supply of gas by the respirator with the respiration of a person in response to a signal indicating the respiration cycle of the person.
A variety of persons such as sick patients and infants benefit from mechanically assisted respiration. In hospitals, respirators are commonly used to assist such persons to breathe. Conventional neonatal respirators deliver gases under pressure in a closed chamber (e.g. the respirator chamber) to babies. Since conventional neonatal respirators are not synchronized with patient respiration, these respirators not infrequently supply gas to infants when the infants are trying to exhale so that the infants are actually breathing against the pressured gas from the respirator. This increases the pressure in the lung and may damage lung tissues. The increase in pressure in the lung may hinder the flow of blood from the brain to the lung, thereby increasing the risk of intracranial hemorrhage.
Because of the above described disadvantages of conventional neonatal respirators, improved designs have been proposed. In one improved design, the change in gas pressure in the chamber is monitored in order to detect spontaneous respiration of the baby. A valve for ventilating the chamber to the atmosphere is then closed or opened in response to detection of inspiration and exhalation by the baby. These neonatal respirators, however, are disadvantageous since they are relatively insensitive to the spontaneous respiration of infants due to a number of factors. The respirator chamber under pressure is relatively large compared to the amount of gas inhaled or exhaled by infants which is usually in the range of five to twenty cubic centimeters. Therefore the inspiration and exhalation of infants will only cause a slight change in pressure of the chamber; such small changes may not be detected by conventional neonatal respirators.
Premature infants frequently experience periodic lapses of respiration known as apnea. Since the improved neonatal respirators described above respond to changes in pressure, such respirators simply cease to function during apnea. Because of this and other disadvantages described above, it is desirable to provide ventilation synchronizers which are more sensitive to spontaneous respiration where the amount of gas inhaled or exhaled is small and which can assist premature infants during apnea.